1. Field of the Invention
The present invention relates to a dual-shaft synchronous transmission device, and more particularly to a dual-shaft synchronous transmission device in which spur structures and crown gear structures are cooperatively assembled to transmit power so as to synchronously rotate the first and second shafts.
2. Description of the Related Art
There are various electronic apparatuses provided with covers or display screens, such as mobile phones, notebooks, PDA, and electronic books. The covers or display screens are pivotally mounted on the electronic apparatuses via pivot pins or rotary shafts, whereby the covers or display screens can be freely rotated and opened/closed under external force. For example, a prior art discloses a rotary shaft structure and another prior art discloses a pivot pin structure.
In order to operate the display module (such as the screen) and/or the apparatus body module of the electronic apparatus in more operation modes and application ranges, a dual-shaft mechanism is provided between the display module and the apparatus body module, whereby the display module and/or the apparatus body module can be operated in different operation modes by different rotational angles. For example, a prior art discloses a dual-shaft hinge device and U.S. Pat. No. 7,512,426 B2 discloses a mobile communications device with synchronizing hinge.
A conventional synchronous transmission device employs multiple conical (or bevel) gears to transmit power for synchronously rotating the two rotary shafts. As well known by those who are skilled in this field, in application of the conical gears for transmitting power, the conical gears must have a sufficiently long cone distance or face distance so that the engaged gears will not slip during transmission of the power. As a result, with the multiple conical gears, the distance between the two shafts of the dual-shaft synchronous transmission device can be hardly as minified as possible. Therefore, the entire transmission mechanism or structure will have a larger volume to occupy more room. Especially, the transmission mechanism applied to the notebook or a mini-type electronic apparatus fails to meet the requirements of lightweight and thinning of the electronic apparatus. This is not what we expect.
According to the above, many shortcomings exist in the conventional dual-shaft synchronous transmission device. It is therefore tried by the applicant to provide a novel dual-shaft synchronous transmission device, which is redesigned to be different from the conventional device and have widened application range. The dual-shaft synchronous transmission device of the present invention can be easily operated to synchronously rotate the first and second shafts. In addition, the distance between the two shafts of the dual-shaft synchronous transmission device is minimized so as to minify the occupied room or volume of the entire transmission device. Also, the engaged gears of the dual-shaft synchronous transmission device of the present invention will not slip during transmission of power so that the transmission delay can be avoided. In addition, the dual-shaft synchronous transmission device of the present invention is applicable to the mini-type electronic apparatus to meet the requirements of lightweight and thinning of the electronic apparatus.